I. Field of the Invention
This invention broadly relates to multimedia conferencing wherein two or more users interact visually and audibly and are able to concurrently share data such as spreadsheets, reports, etc. More particularly, the present invention pertains to multimedia conferencing in which two or more users interact with each other through the use of terminal equipment having audio and video input/output capabilities. Most particularly, the present invention is directed to a process for converting an existing or ongoing point-to-point multimedia telephone call into a bridged call wherein the point-to-point call terminal devices are connected to a common video bridge such as a multipoint control unit (MCU) while maintaining between the participants a continuous exchange of audio information throughout the conversion process.
II. Discussion of Background Art
Recent developments in telecommunications provide the capability of video calling wherein two users communicate and interact with each other over a direct transmission link or telephone line, such as an Integrated Services Digital Network (ISDN) line, via the use of terminal equipment having audio and video input/output capabilities. In general, the terminal equipment used in video calling is a workstation containing a microphone and speaker for audio exchange, a video camera and screen for video exchange and a computer for the exchange of data which may comprise, for example, reports, spreadsheets, graphs, etc.
Video call information is commonly configured into a data string format comprised of two bearer (B) channels (with each channel carrying either 56 or 64 kilobits per second (kb/s)) and a signal channel (D) of 16 kb/s; this format is commonly referred to as 2B+D or Basic Rate Interface (BRI) format. Video call information can alternatively be configured into a Primary Rate Interface (PRI) format, also referred to as a 23B+D format, which is a data string comprised of 23 bearer (B) channels and a signal channel (D) of 64 kb/s. For standard data configuration most video calls utilize the H.320 video telephone protocol which configures the initially connected bearer channel to carry that portion of the data string representing all of the audio and data information (reports, spreadsheets, etc.) as well as a small portion of the video information, and configures the later-connected bearer channel(s) to carry the remainder of the video information.
In a video call, two users can interact directly via a point-to-point connection either through a local central office for a local call, or through a main switching station for a toll call. Users may also interact indirectly via use of a video bridge, such as multipoint control unit (MCU), wherein each workstation is connected to and shares a common MCU. When an MCU is used, such interaction is referred to as multimedia conferencing and, through the use of additional ports on the MCU, one or numerous additional third party users to a multimedia conference can be accommodated in the conference by connecting additional workstations to the MCU.
The basic features of an MCU are described, by way of example, in M. J. Koenig, et. al., "MCUs Help Take The Worry Out Of Being There", AT&T Technology Products, Systems and Services, Vol. 9, No. 4, Winter, 1994, pages 12-15, the entirety of which is incorporated by reference herein. Basically, an MCU synchronizes a multiplexed data bit stream comprised of voice, video and data which originates from each workstation endpoint, ensures a compatible set of audio and video parameters for the video conference from the options communicated by the control sequences received from the other workstation endpoints, and then decodes and sums the audio streams from all users for broadcast to the conference call participants.
To initiate a video conference call between, for example, three separate workstations having a user or participant at each, a reservation must first be made to reserve the necessary ports on an MCU to which the participating workstations will be connected. Thus, for a multimedia conference the number of connected workstations will be specified along with the starting time of the conference so that the system or network to which the MCU is connected can accommodate the intended number of participants at the pre-selected conference starting time.
Such an above-described technique, wherein reservations must first be made for the desired number of ports on an MCU, is readily employed when the number of participants and the approximate starting time for a multimedia conference are known. However, if a multimedia call is first commenced between two participants, i.e. a point-m-point call between user A and user B, and during that point-to-point call it becomes desirable or necessary to include at least a third participant, i.e. user C, there is at present no known technique for uninterruptedly accommodating the connection of user C's workstation to the ongoing point-to-point call. Thus, in order to include user C, the existing point-to-point multimedia call between users A and B must first be terminated, a reservation for the desired number of ports and time on an MCU must be made, and a new conference call then initiated between all intended participants, i.e. users A, B and C. As will be appreciated, such a disruption to the existing and ongoing point-to-point video call between users A and B is not only inconvenient but is likely to break the flow of the discussion and/or exchange of information between users A and B, and thereby defeat the very reason for desiring the addition of one or more new participants to the conference.